The invention relates to a device for measuring the radial forming forces in metal spinning latches, whose spin rolls are attached to spindles, which are supported in bearings in a stationary bearing housing.
Metal spinning is a method for the cold shaping of hollow cylindrical components, in which spinning rolls are used so as to make punctuate force engagement along helical lines so that part of the thickness of the tube wall is stretched in the length direction of the tube. As it is radially displaced by the thrust force the material flows with a shear motion away in an axial direction. Spinning lathes are generally equipped with two or three symmetrically arranged spinning rolls which generally maintain a balance between the relatively high radial forces.
If the tool geometry is correctly selected and the process data are well matched tubular workpieces may be spun with an extraordinary degree of precision, and for instance within a single cross section it is possible to keep deviations in the wall thickness under 0.01 mm.
The relatively complex forming phenomena taking place during metal spinning are however hardly to be understood. If the forming parameters are correct, the workpiece is in order. If they depart from the intended value at any position, the effects will only be able to be seen in the finished workpiece. A certain indication of what is taking place during forming at a given time may be seen from the forces occurring at the individual spinning rolls. If they are measured, the metal spinning operation may be directly and continuously monitored and corrected if necessary or automatically controlled. In this respect it is sufficient if only one of the three force components is measured. It would be obvious to measure the radial forces. For the sake of getting a better overall picture and for matching it is however necessary for each spin roll to be provided with its own measuring means.
Conventionally such forces are measured with the aid of wire strain gages (DMS). The elastic deformation caused by the forces on the object are transferred to the DMS attached in an isolated manner to the object and change the electrical resistance thereof. The drop in voltage resulting from this serves as a measurement of the forces.
In accordance with another familiar method, forces are measured using piezoelectric sensors. In this case the effect of certain crystals is used in order, under the action of thrusts or strains in certain directions, to build up electrical charges at the ends of their polar axes.
These two methods of measurement are not particularly well suited to the measurement of radial forces during metal spinning. On the one hand difficulties occur if such methods are applied to rotating machine parts such as the spinning rolls or their spindles or as regards the transmission of signals from rotating to stationary parts. On the other hand under rough production conditions it is hardly possible to ensure reliable operation of either system. In the case of force measurement with piezoelectric sensors the very high forces during metal spinning would be a problem yet to be resolved.